Urethane can be catalytically or thermally decomposed to form corresponding isocyanates which are important key materials in the polyurethane (PU) industry as well as in the pharmaceutical industry. Hence, use of toxic phosgene can be avoided in the preparation of isocyanates from urethane. One efficient way to prepare urethane is oxidative alkoxycarbonylation of primary amine, which can be represented by the following general reaction equation: ##STR1##
In this formula, R is the organic radical of the corresponding primary amino group-containing compound, R' is the organic radical of the hydroxyl group-containing compound, and x is an integer.
In the prior art, the disclosed catalyst system for this process is mainly group VIIIB metals of the periodic table, in combination with nitrogen-or phosphorous-containing compounds or halides as promoters.
U.S. Pat. No. 4,297,501 discloses a catalyst system comprising halides of a noble metal of the VIIIB group of the periodic table, and a compound capable of undergoing redox reactions. Also, European Pat. Appl. 083,095 discloses a process for preparing urethane in the presence of a catalyst system comprising the Pt group metals and halides of alkali metals or alkaline earth metals.
The fact that the disclosed patents use expensive noble metal catalysts partially diminishes the commercial interest in the known processes.